Author Topic: L5 Preamp Compressor Circuit Issue  (Read 338 times)

jfurgason

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L5 Preamp Compressor Circuit Issue
« on: May 14, 2022, 12:17:47 PM »
Hi all,

So I've been wrestling with the L5 preamp for a while and I have finally got it about 90% working, but the compressor is behaving super strangely.  It sounds super fuzzed out when it engages and is highly sensitive.  It will also sometimes trigger even when the switch is off.  I've checked all the voltages and only found two components out of spec with expected values.

IC11
1 - 0V
2 - 0V
3 - 0V
4 - -15.1V
5 - -14.9V
6 - -0.06V (should be 0.23V)
7 - 14.74V
8 - 0V

Q1
D - 14.97V (expected)
S - 0.05V (should be 0.02V)
G - -0.06V (should be -0.02)

I originally had bad 3080 chips in IC10 and IC11, but did replace them with chips from SmallBear a while ago. IC10 gives all the correct voltages so I don't think the problem is in the 3080 but I'm not sure where to look at this point. I've also tried switching out Q1, 2 and 3 (currently using a surface-mount 5457 with an adapter on Q1). I appreciate any insight anyone can offer on this one

Thanks!

mauman

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Re: L5 Preamp Compressor Circuit Issue
« Reply #1 on: May 15, 2022, 04:29:20 PM »
Drew just built one, maybe ask over in this thread?  https://www.madbeanpedals.com/forum/index.php?topic=33813.0

Drew Hallenbeck

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Re: L5 Preamp Compressor Circuit Issue
« Reply #2 on: May 16, 2022, 10:45:50 AM »
It's such a complex circuit and there are any number of things that could throw it's performance out of whack....
Did you follow the calibration instructions as far as injecting a 1kHz signal at the appropriate voltage and setting the distortion trimmer first?
Also, make sure you have the master volume all the way up and the compression at about 2/3 before adjusting the compression trimmer.
Building with my daughter and occasionally selling as "Daddy Daughter Pedal Works"
Not for any real profit, just trying to have a self-funding hobby.

jfurgason

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Re: L5 Preamp Compressor Circuit Issue
« Reply #3 on: May 16, 2022, 02:07:09 PM »
Yep, I did the distortion calibration and was seeing the correct AC voltage pin 6 on IC10. I canít seem to get the compressor trim to get the right value, at its maximum and minimum ends Iím seeing between 0.244 and 0.29 VAC.  Iíve reflowed what I can reach, rewired everything,  and rechecked all resistor values and remeasured all chips and transistors. Power supply is still good, getting the proper +/-15V at the test points. Here are any readings not in spec with what voltage is expected per Aionís voltage doc.

All DC voltages
IC 4 (Iím using OPA2134 instead of 4558)
1 = 0V (should be -0.02V)
2 = 0
3 = 0
4 = -15.17
5 = 0
6 = 0
7 = 0.009
8 = 14.96

IC 5 (OPA2134)
1 = 0 (should be 0.01)
2 = 0 (should be 0.01)
3 = 0 (should be 0.01)
4 = -15.17
5 = 0 (should be 0.01)
6 = -0.9 (should be 0)
7 = 0
8 = 14.96

IC6 (OPA2134)
1 = 0 (should be -0.05)
2 = 0
3 = 0
4 = -15.17
5 = 0
6 = 0
7 = 0 (should be -0.06)
8 = 14.96

IC7 (OPA2134)
1 = 0 (should be -0.04)
2 = 0
3 = 0
4 = -15.17
5 = 0
6 = 0
7 = 0 (should be -0.05)
8 = 14.96

IC8 (OPA2134)
1 = 0 (should be -0.03)
2 = 0
3 = 0
4 = -15.17
5 = 0
6 = 0
7 = 0 (should be -0.02)
8 = 14.96

IC11 (CA3080)
1 = 0
2 = 0
3 = 0
4 = -15.17
5 = -14.62
6 = -0.09 (should be 0.23)
7 = 14.96
8 = 0

IC12 (OPA2134)
1 = -0.003 (should be 0)
2 = 0
3 = 0
4 = -15.17
5 = 0
6 = 0
7 = 0.004 (should be 0)
8 = 14.96

IC13 (LM741)
1 = -15.16
2 = 0
3 = 0
4 = -15.16
5 = -15.16
6 = 0.008 (should be 0.02)
7 = 14.96
8 = 0

All other ICs are showing what is expected

Transistors
Q1 (MMBF5457)
D = 14.96
S = -0.08 (should be 0.02)
G = -0.1 (should be -0.02)

Q2 (2N3906)
1 = 0
2 = -0.006 (should be 0)
3 = 14.58

Q3 (MPSA13) these values all look correct
1 = -15.17
2 = -14.43
3 = -0.369

QX1
1 = 0.291 (should be 0.4)
2 = 0.792 (should be 0.9)
3 = 14.91

QX2
1 = -0.332 (should be -0.22)
2 = 0.29 (should be 0.4)
3 = 13.48

Tested on a 9VAC supply with the distortion trimmer properly calibrated. These were the values that jumped out to me, some of the discrepancies are probably within acceptable variance, but Iím including them just to be through. Maybe this helps point to a problem area? I might try subbing in 4558 chips for my 2134 chips and see if that does anything. I may also try new Q1-3 as well. Appreciate any help or insight on this one
Cheers

jfurgason

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Re: L5 Preamp Compressor Circuit Issue
« Reply #4 on: May 31, 2022, 06:10:48 PM »
Just popping back in to the thread to say that Iíve resolved the issue and can finally take this one off the troubleshooting bench. I ended up replacing all my 2134 chips for 4558s as well as new Q1-3 and new 3080s. I wasnít very scientific and just replaced everything at once but it now works like a charm!

gordo

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Re: L5 Preamp Compressor Circuit Issue
« Reply #5 on: June 01, 2022, 06:09:25 PM »
Doesn't matter how you get it there, as long as it works  ;D
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